Cardiopulmonary distress is the major cause of death in the neonatal period. Generally the approach to management has been similar to that in the adult and has included methods to increase cardiac output. Recently we have shown that oxygen consumption per kg of weight increases dramatically after birth and is paralleled by a marked increase in cardiac output. Within 10 weeks there is a marked reduction in oxygen consumption and cardiac output in relation to body weight. In view of the high resting cardiac output required to provide oxygen to the tissues, there is very little reserve in response to stress. We propose to consider therapy of circulatory failure in the neonatal lamb in the context of: 1) improving oxygen delivery to the tissues by exchange transfusion of the fetal blood in the neonate, with adult blood, so as to shift the oxygen equilibration curve to the right and increase P50 of the blood; or 2) decreasing oxygen requirements of the body by use of muscle relaxants, sedation and by assisting ventilation. The potential beneficial effects of these procedures will be evaluated in induced hypoxia, hemorrhage, prematurity, left-to-right and right-to-left shunts, and induced left ventricular outflow obstruction.